The present invention relates to semiconductor diodes. In particular, the present invention relates to a Schottky diode with reduced reverse leakage current.
Diodes are a fundamental electronic building block. Their ability to restrict current flow to substantially one direction is a critical property relied upon in virtually every electronic circuit manufactured, from the smallest power supply to the largest industrial process controller. While unidirectional current flow is an ideal diode property, all diodes are subject to undesirable reverse leakage current.
The reverse leakage current is current that flows xe2x80x9cbackwardsxe2x80x9d through a reverse biased diode (i.e., when the diode should ideally be off or completely nonconducting). In other words, even when the diode is reversed biased, the diode allows a small amount of current (the reverse leakage current) to flow.
In most instances, the reverse leakage current is detrimental to system performance. As one example, in a sampling analog to digital converter, the reverse leakage current may result in charge allowed to dissipate off of a holding capacitor. As a result, the digital conversion process has a limited amount of time in which to complete a suitably accurate conversion. The longer the conversion delay, the less accurate the final result, as reverse leakage current continues to remove charge from the holding capacitor. Generally, the reverse leakage current results in undesired power dissipation to no useful end.
Because a portion of the reverse leakage current arises from the physical junction interaction of the Schottky metal and semiconductor materials (in a Schottky diode) or the p and n semiconductor materials (in a pn diode), a certain amount of reverse leakage current is unavoidable. However, experiments show that the particular arrangement or layout of the semiconductor materials that form the diode also can also contribute to the reverse leakage current. Regardless of its source, the reverse leakage current in virtually every instance introduces undesirable characteristics in the operation of an efficient electronic device.
A need has long existed in the industry for a diode that address the problems noted above and others previously experienced.
A preferred embodiment of the present invention provides a Schottky diode formed from a conductive anode contact, a semiconductor junction layer supporting the conductive contact and a base layer ring formed around at least a portion of the conductive anode contact. In particular, the base layer ring has material removed to form a base layer material gap (e.g., a vacuum gap) adjacent to the conductive anode contact. A dielectric layer is also provided to form one boundary of the base layer material gap. The conductive contact may be, as examples, a layer of Titanium, a layer of Platinum, and a layer of Gold, or a layer of Platinum, a layer of Titanium, a second layer of Platinum, and a layer of Gold.
The base layer material gap is preferably sized in accordance with the expected extent of a reverse bias depletion region in the semiconductor layer. In other words the base layer material gap is generally large enough to present an absence of base layer material to the depletion region above the semiconductor layer.
Another preferred embodiment of the present invention provides a method for fabricating a diode. The method includes the steps of creating a semiconductor layer on a substrate, creating a base layer on the semiconductor layer, and creating a dielectric layer on the base layer. In addition, the, method removes a portion of the dielectric layer to form a via through the dielectric layer to the base layer, laterally removes a portion of the base layer underneath the dielectric layer and through to the. semiconductor layer at the via, and creates a conductive anode contact in the via supported by the semiconductor layer. The conductive anode contact thereby bounds a base layer gap between the conductive anode contact and the base layer ring.